This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
The acquisition and rendering of 4D light-field data, which can be viewed as a sampling of a 4D light field (i.e. the recording of light rays as explained in FIG. 1 of the article: “Understanding camera trade-offs through a Bayesian analysis of light field projections” by Anat Levin et al., published in the conference proceedings of ECCV 2008) is an hectic research subject.
Indeed, compared to classical 2D images obtained from a camera, 4D light-field data enable a user to have access to more post processing features that enhance the rendering of images and/or the interactivity with the user. For example, with 4D light-field data, it is possible to perform with ease refocusing of images a posteriori (i.e. refocusing with freely selected distances of focalization meaning that the position of a focal plane can be specified/selected a posteriori), as well as changing slightly the point of view in the scene of an image. The acquisition of 4D light-field data can be done by different techniques (for example via the use of plenoptic camera, as depicted in document WO 2013/180192 or in document GB 2488905, or via the use a camera array as depicted in document WO 2014/149403).
In the state of the art, there are several ways to represent (or define) 4D light-field data. Indeed, in the Chapter 3.3 of the Phd dissertation thesis entitled “Digital Light Field Photography” by Ren N g, published in July 2006, three different ways to represent 4D light-field data are described. Firstly, 4D light-field data can be represented, when recorded by a plenoptic camera by a collection of micro-lens images. 4D light-field data in this representation are named raw images (or raw 4D light-field data). Secondly, 4D light-field data can be represented, by a set of sub-aperture images. A sub-aperture image corresponds to a captured image of a scene from a point of view, the point of view being slightly different between two sub-aperture images. These sub-aperture images give information about the parallax and depth of the imaged scene. Thirdly, 4D light-field data can be represented by a set of epipolar images (see for example the article entitled: “Generating EPI Representation of a 4D Light Fields with a Single Lens Focused Plenoptic Camera”, by S. Wanner et al., published in the conference proceedings of ISVC 2011).
Usually, 4D light-field data can be used for displaying at least one 2D image in which refocusing a posteriori can be done (i.e. the display device is a conventional display device). But, it is also possible to display these 4D light-field data via a light field display device as the one depicted in document U.S. Pat. No. 8,933,862, or in the document U.S. Pat. No. 8,416,289. In a variant, the light field display device can be the one depicted in the article entitled “A Compressive Light Field Projection System” by M. Hirsch, G. Wetzstein, R. Raska, published in the conference proceedings of SIGGRAPH 2014.
In order to protect the delivering of 4D light-field data, one skilled in the art is urged to use classical Digital Right Management (DRM) techniques. For example, in the case that a Video On demand system provides 4D light-field data (intended to be either displayed at a light field content or a to be used for extracting 2D content to be displayed), one skilled in the art could have use the technique described in document WO 2006/053804. Hence, a degraded 4D light-field data that is obtained from a wavelet coefficient basis encoding technique, can still be viewed (but in a degraded way). Therefore, the user can decide to pay for having access to a non-degraded version of the received degraded 4D light-field data, in the same way as in document WO 2006/053804.
The present technique provides an alternative to this approach, that is less complex to implement.